This invention relates to a repeater arrangement for use in repeating a sequence of input multiplexed signals to produce a sequence of output multiplexed signals in a digital transmission network.
A conventional repeater arrangement of the type described is supplied with a sequence of input multiplexed signals divisible into a sequence of multiframes each of which is subdivided into a plurality of subframes. Each subframe is composed of a predetermined number of time slots assigned to channels, respectively. A data signal unit is arranged in each time slot determined for each channel. Herein, it is to be noted that such data signal units are not always produced at the same bit rate but usually at bit rates which are different from one another. In order to equalize the different bit rates, one or more stuff pulses are arranged in a predetermined one of the subframes of each multiframe.
In the repeater arrangement, such an input multiplexed signal sequence is demultiplexed by a demultiplexer into a plurality of demultiplexed signals assigned to the respective channels. The demultiplexed signals are delivered to external devices and are memorized in a plurality of elastic memories, respectively, which may be operable as an intermediate circuit and which are in one-to-one correspondence to the channels. Such write-in operations of the demultiplexed signals are carried out by the use of a plurality of write-in clock pulses each of which is inhibited at a time instant at which each stuff pulse is located. As a result, the demultiplexed signals are written into the respective elastic memories with the stuff pulses destuffed. The memorized demultiplexed signals are read out of the elastic memories as reproduced demultiplexed signals in synchronism with readout clock pulses which are given from voltage-controlled oscillators coupled to phase comparators so as to form phase-locked loops, respectively. The phase comparators compare the readout clock pulses with the write-in clock pulses to produce phase control signals and to thereby control the voltage-controlled oscillators, respectively.
The reproduced demultiplexed signals are sent to a multiplexer to be multiplexed into a sequence of output multiplexed signals with stuff pulses added thereto.
As is readily understood from the above, each of the phase-locked loops is necessary for every one of the channels. This shows that the phase-locked loops would increase in number with an increase of the channels and that the conventional repeater arrangement becomes more expensive as the number of the channels increases.
In addition, the readout clock pulses are controlled by the phase comparators in relation to the write-in clock pulses which are inhibited at the time instants of the stuff pulses. Inasmuch as the readout clock pulses are derived from the write-in clock pulses which are inhibited at the time instants for the stuff pulses, phases of the readout clock pulses subtly fluctuate due to pulse stuffing and cause phase differences to occur in each of the readout clock pulses. Such phase differences in the readout clock pulses give rise to phase jitters and result in accumulation of stuff jitters which come from the phase jitters.